Photosyntesis & Plants - Practicals Flashcards
Starch Test Explained
7 marks
Place the leaf in boiling water for 30 seconds – this kills it, stopping any further chemical reactions.
Place the leaf in boiling ethanol – removes the chlorophyll making the leaf paler in colour.
Dip the leaf in water – this softens it.
Spread the leaf onto a white tile and add iodine to test for the presence of starch.
Why do we place the leaf in boiling Ethanol during the Starch Test?
(2 marks)
Remove the chlorophyll making the leaf paler in colour.
What do we use to test for Starch?
1 mark
Iodine
Safety Rules during Starch Test
2 marks
Wear goggles throughout experiment.
Ensure Ethanol is not exposed to a naked flame.
Why shouldn’t you expose Ethanol to a naked flame?
1 mark
It’s highly flammable.
If a plant has Photosynthesised what will it test positive for?
(1 mark)
Starch
Starch Test Simplified
5 marks
Place Leaf in
- Boiling Water 30 seconds
- Boiling Ethanol
- Dip in water
- Spread on white tile and add iodine
Starch Test Results
3 marks
Starch present - iodine will change from yellow-brown to blue-black.
Starch absent - iodine will remain yellow-brown.
What will iodine tell us about a leaf?
1 mark
If it contains Starch.
If starch is present the iodine will change from yellow-brown to?
(1 mark)
Blue-black
If starch is absent the iodine what will happen to the iodine?
(1 mark)
It will remain yellow-brown/orange.
Colour of Aqueous Iodine Solution
1 mark
Yellow-brown/orange
How long should you place the leaf in water during the Starch Test?
(1 mark)
30 seconds
Why should you place the leaf in boiling water during the Starch Test?
(2 marks)
To kill it - stopping further chemical reactions.
Why should you dip the leaf in water after placing it in boiling Ethanol during the Starch Test?
(1 mark)
Soften it.
Destarching a Plant:
2 marks
Place Plant in the dark for at least 48 hours
- during this time any starch will be removed or used.
How can you Test if a Plant has been fully Destarched?
2 marks
Testing a leaf for starch through the Starch Test.
If iodine remains yellow-brown all the starch has successfully been removed.
How many steps are there in the Starch Test?
1 mark
4 steps
Before what is it important to Destarch a Plant?
1 mark
Before carrying out any photosynthesis practical.
Investigating the Need for Chlorophyll in Photosynthesis: Procedure Simplified
(6 marks)
Destarch a Variegated Plant.
Make a drawing of the leaf.
Place the plant in bright light - 7 hours
Test the leaf for starch using the Starch Test.
Make another drawing of the leaf - showing areas of the leaf that tested positive negative for starch.
Investigating the Need for Chlorophyll in Photosynthesis: Results
(3 marks)
Only the areas that contained Chlorophyll will Photosynthesise
Therefore test positive for starch.
Showing Chlorophyll is necessary for Photosynthesis.
Investigating the Need for Chlorophyll in Photosynthesis: Procedure Explained
(6 marks)
Destarch a Variegated Plant - partly green and partly white.
Make a drawing of the leaf.
Place the plant in bright light - 7 hours
Test the leaf for starch using the Starch Test (4 steps)
Make another drawing of the leaf - showing areas of the leaf that tested positive + negative for starch.
Variegated Plant
3 marks
Partly green and partly white - due to the presence of 2 kinds of plant tissue.
(no chlorophyll development in certain areas)
How long should you place a plant in bright light when Investigating the Need for Chlorophyll in Photosynthesis?
(1 mark)
7 hours.
Only what areas will Photosynthesise?
1 mark
Containing Chlorophyll.
Investigating the Need for CO2 in Photosynthesis: Procedure
6 marks
Destarch a Plant.
Expose 1 leaf to Sodium Hydroxide = will absorb CO2 from the surrounding air.
Expose another leaf to water (control experiment) = will not absorb CO2 from the surrounding air.
Place the plant in bright light - 7 hours.
Test both leaves for starch using the Starch Test.
A Destarched leaf exposed to Sodium Hydroxide will do what?
1 mark
Absorb CO2 from the surrounding air.
Will a Destarched leaf exposed to Water absorb CO2 from surrounding air?
(1 mark)
No - will not absorb CO2 from the surrounding air.
Will a Destarched leaf exposed to Sodium Hydroxide absorb CO2 from surrounding air?
(1 mark)
Yes - will absorb CO2 from the surrounding air.
Investigating the Need for CO2 in Photosynthesis: Results
3 marks
Only the leaf that has been exposed to CO2 will Photosynthesis
Therefore test positive for starch.
Showing CO2 is necessary for Photosynthesis .
Is CO2 necessary for Photosynthesis?
1 mark
Yes.
Is Chlorophyll necessary for Photosynthesis?
1 mark
Yes.
